Addons: Only some .zips will install
You can install from zip directly if the zip is either:


a zipped single .py file

  addon_name.zip
       |  
       addon_name.py   

a zipped folder, important that it's not a zip that contains a folder first.


these will work because the folder structure is at the expected level. The __init__.py is directly inside the zip ("top level").


https://github.com/nortikin/sverchok
https://github.com/JacquesLucke/animation_nodes





  addon_name.zip
       |  
       addon_foo.py   
       __init__.py


this will also work

  addon_name.zip
       |  
       addon_name_folder
              |
              addon_foo.py   
              __init__.py



for instance: this zip will fail, because the add-on folder is nested too deep, there's another folder inside the zip: 


https://github.com/zeffii/TubeTool  (this is a link to a branch that first has an extra level of folder nesting)
Github will generate a zip from that repo that looks like this:  





  repository_name.zip
       |  
       repository_name_folder
            |
            first_folder_in_repo
                    | 
                    addon_foo.py   
                    __init__.py



Zipped add-ons with a structure that doesn't work with the install-from-file feature may or may not have a good reason for being that way.